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Monday, August 5, 2013

Making patterned mirrors and ITO glass with a thermal evaporator

I've put enough work into my thermal evaporator project so that I can actually start using it to create thin films. For my first test, I make some aluminum mirrors on glass, and also coated glass with ITO (Indium Tin Oxide). The mirrors look nice, but the ITO was not conductive -- more research required.

ITO is not usually evaporated- I'll ask some coatings guys I know about what might be happening. I saw some recommendations on your YouTube feed. Annealing in oxygen would probably make things no better; good ITO heated in air loses conductivity. There is a critical amount of 'oxygen vacancies' you need. Nitrogen might be better, but I am dubious that this is the problem.

I have some organic semiconductors I can send you if you want to make some films and experiment. A good first experiment, before you try TFTs or OLEDs, is to make a film and watch its conductivity change in response to light. Do you have a ResearchGate profile? I have about a dozen publications in the area of organic semiconductors and devices, if you want to see them.

OK, Ben, this is what I learned about evaporating ITO: one of the biggest issues with evaporation is that complex targets do not maintain stoichiometry. At the high temperatures involved, often phase segregation occurs and you are stuck with the relative evaporation rates of the different elements/materials. Also, oxygen vacancies are the major “dopant” in ITO generating charge carriers, so controlling the oxygen stoichiometry is critical to getting transparent coatings that are still conductive. I'm not sure evaporation will work unless someone has all the details dialed in. Time to build an RF sputtering chamber...

David, I really appreciate the advice. I've given up on the idea of evaporating ITO, and I'm surprised that places like Lesker sell ITO pellets intended for evaporation. I've already started on the sputter gun, but I'm hoping to use DC since I don't have a high power RF power supply yet. I don't have a ResearchGate account, but I'd be interested in hearing about your research and using your organic semiconductors. Talk to you later -Ben

Shoot me an email on Google+. I have some single molecule semiconductors that can be drop cast, or evaporated, and at least a small vial of one of the polythiophenes. Some single molecules I have make good OLEDs, others make good transistors. I might have some MEH-PPV that you can make OLEDs or OLECs from. I'll dig around. Chemists never get rid of anything.